U.S. patent number 11,440,799 [Application Number 16/332,868] was granted by the patent office on 2022-09-13 for carbon material and method for manufacturing carbon material.
This patent grant is currently assigned to KYOTO UNIVERSITY, SUMITOMO ELECTRIC INDUSTRIES, LTD.. The grantee listed for this patent is KYOTO UNIVERSITY, SUMITOMO ELECTRIC INDUSTRIES, LTD.. Invention is credited to Tomoyuki Awazu, Kouji Hidaka, Masatoshi Majima, Yoshiki Nishibayashi, Toshiyuki Nohira, Kouji Yasuda.
United States Patent |
11,440,799 |
Awazu , et al. |
September 13, 2022 |
Carbon material and method for manufacturing carbon material
Abstract
A carbon material has at least either a peak related to diamond
bonds, or a peak related to diamond-like bonds, appearing in a
range of 1250 to 1400 cm.sup.-1 in a spectrum measured by Raman
scattering spectrometry, and a full width at half maximum of a
maximum peak, or each of full widths at half maximum of the maximum
peak and a second largest peak, among peaks appearing in the range
of 1250 to 1400 cm.sup.-1, has a signal less than 100
cm.sup.-1.
Inventors: |
Awazu; Tomoyuki (Itami,
JP), Majima; Masatoshi (Itami, JP),
Nishibayashi; Yoshiki (Itami, JP), Nohira;
Toshiyuki (Kyoto, JP), Yasuda; Kouji (Kyoto,
JP), Hidaka; Kouji (Kyoto, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
SUMITOMO ELECTRIC INDUSTRIES, LTD.
KYOTO UNIVERSITY |
Osaka
Kyoto |
N/A
N/A |
JP
JP |
|
|
Assignee: |
SUMITOMO ELECTRIC INDUSTRIES,
LTD. (Osaka, JP)
KYOTO UNIVERSITY (Kyoto, JP)
|
Family
ID: |
1000006554861 |
Appl.
No.: |
16/332,868 |
Filed: |
November 21, 2017 |
PCT
Filed: |
November 21, 2017 |
PCT No.: |
PCT/JP2017/041844 |
371(c)(1),(2),(4) Date: |
March 13, 2019 |
PCT
Pub. No.: |
WO2018/097134 |
PCT
Pub. Date: |
May 31, 2018 |
Prior Publication Data
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|
|
Document
Identifier |
Publication Date |
|
US 20190359487 A1 |
Nov 28, 2019 |
|
Foreign Application Priority Data
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|
|
|
|
Nov 22, 2016 [JP] |
|
|
JP2016-227083 |
Mar 15, 2017 [JP] |
|
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JP2017-050531 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C25B
1/14 (20130101); C01B 32/05 (20170801); C25B
1/135 (20210101); C25B 11/043 (20210101); C01P
2002/82 (20130101) |
Current International
Class: |
C01B
32/05 (20170101); C25B 11/043 (20210101); C25B
1/135 (20210101); C25B 1/14 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2729091 |
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Dec 2009 |
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CA |
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104389012 |
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Mar 2015 |
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CN |
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104562073 |
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Apr 2015 |
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CN |
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104562073 |
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Apr 2015 |
|
CN |
|
2016-505490 |
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Feb 2016 |
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JP |
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2016-89230 |
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May 2016 |
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JP |
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2016089230 |
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May 2016 |
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JP |
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Other References
Li et al, "A One-Pot Synthesis of Hydrogen and Carbon Fuels from
Water and Carbon Dioxide," Adv. Energy Mater. 2015, 5, 1401791
(Year: 2015). cited by examiner .
Ito et al, "Electrochemical Formation of Thin Carbon Film from
Molten Chloride System," 1992 Proceedings of the Electrochemical
Society, vol. 1992-16 57 (Year: 1992). cited by examiner .
Lou et al., Synthesis of Large-Size Diamonds by Reduction of Dense
Carbon Dioxide with Alkali Metals (K, Li), J. Phys. Chem. B 2004,
108, 4239-4241. cited by examiner .
Nohira, Toshiyuki, "Electrolytic synthesis of diamond in molten
salts," 2013 Fiscal Year Final Research Results Report
(Kakenhi-Project), Project/Area No. 24655192, Jun. 16, 2014, 4
pages. cited by applicant .
CN Office Action dated Mar. 31, 2021 in Chinese Application No.
201780056604.X. (with attached English-language translation). cited
by applicant .
Zhengsong Lou et al., "Synthesis of diamond and carbon materials by
chemical reduction of carbon dioxide", Beijing: Beijing University
of Posts and Telecommunications Press, Dec. 31, 2013, pp. 39-48.
cited by applicant .
English-language translation of Zhengsong Lou et al., "Synthesis of
diamond and carbon materials by chemical reduction of carbon
dioxide", Beijing: Beijing University of Posts and
Telecommunications Press, Dec. 31, 2013, pp. 39-48, previously
submitted. cited by applicant .
English-language translation of Nohira, Toshiyuki, "Electrolytic
synthesis of diamond in molten salts," 2013 Fiscal Year Final
Research Results Report (Kakenhi-Project), Project/Area No.
24655192, Jun. 16, 2014, 4 pages, previously submitted. cited by
applicant.
|
Primary Examiner: Jain; Salil
Attorney, Agent or Firm: Faegre Drinker Biddle & Reath
LLP
Claims
The invention claimed is:
1. A method for manufacturing a carbon material, the method
comprising the step of, in a state where a cathode having a
roughened surface and an anode are disposed in a molten salt
electrolytic solution containing carbonate ions and hydroxide ions
in a molten salt, performing electrolytic reduction of the
carbonate ions and the hydroxide ions contained in the molten salt
electrolytic solution, to generate a carbon material on the
cathode, wherein the cathode having the roughened surface is a
cathode having a surface roughened by diamond abrasive grains
having a grain diameter of 20 nm to 5 .mu.m or silicon carbide
abrasive grains having a grain diameter of 20 nm to 5 .mu.m,
wherein the carbon material has at least either a peak related to
diamond bonds, or a peak related to diamond-like bonds, appearing
in a range of 1250 to 1400 cm.sup.-1 in a spectrum measured by
Raman scattering spectrometry, and wherein a full width at half
maximum of a maximum peak, or each of full widths at half maximum
of the maximum peak and a second largest peak, among peaks
appearing in the range of 1250 to 1400 cm.sup.-1, has a signal less
than 100 cm.sup.-1.
2. The method according to claim 1, wherein the cathode having the
roughened surface is the cathode having the surface roughened by
diamond abrasive grains.
3. The method according to claim 1, wherein the molten salt is a
molten salt containing at least one type of cation selected from
the group consisting of alkali metal ions and alkaline earth metal
ions, as a cation, and a halide anion as an anion.
Description
TECHNICAL FIELD
The present disclosure relates to a carbon material and a method
for manufacturing a carbon material.
This application claims priority on Japanese Patent Application No.
2016-227083 filed on Nov. 22, 2016 and Japanese Patent Application
No. 2017-050531 filed on Mar. 15, 2017, the entire contents of
which are incorporated herein by reference.
BACKGROUND ART
As a method for manufacturing diamond, for example, Patent
Literature 1 proposes a method in which, under a carbon dioxide
atmosphere, electrolytic reduction of carbon dioxide is performed
in a molten salt while a cathode voltage is controlled.
CITATION LIST
Patent Literature
PATENT LITERATURE 1: Japanese Laid-Open Patent Publication No.
2016-89230
SUMMARY OF INVENTION
One aspect of the present disclosure is directed to a carbon
material having at least either a peak related to diamond bonds, or
a peak related to diamond-like bonds, appearing in a range of 1250
to 1400 cm.sup.-1 in a spectrum measured by Raman scattering
spectrometry, wherein
a full width at half maximum of a maximum peak, or each of full
widths at half maximum of the maximum peak and a second largest
peak, among peaks appearing in the range of 1250 to 1400 cm.sup.-1,
has a signal less than 100 cm.sup.-1.
Another aspect of the present disclosure is directed to a method
for manufacturing a carbon material, the method comprising the step
of, in a state where an anode and a cathode having a roughened
surface are disposed in a molten salt electrolytic solution
containing carbonate ions and hydroxide ions in a molten salt,
performing electrolytic reduction of the carbonate ions and the
hydroxide ions contained in the molten salt electrolytic solution,
to generate a carbon material on the cathode.
Still another aspect of the present disclosure is directed to a
method for manufacturing a carbon material, the method comprising
the step of, in a state where an anode and a cathode are disposed
in a molten salt electrolytic solution containing carbonate ions
and hydroxide ions in a molten salt, performing electrolytic
reduction of the carbonate ions and the hydroxide ions under a
condition that reaction in which sp.sup.2 carbon atoms and adsorbed
hydrogen atoms are reacted with each other to generate methane gas
is promoted, to generate a carbon material on the cathode.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a diagram schematically illustrating the principle of
methods for manufacturing a carbon material.
FIG. 2 is a diagram schematically illustrating an example of an
electrolytic reduction apparatus used in the method for
manufacturing a carbon material.
FIG. 3 is a spectrogram showing Raman spectra of deposits obtained
by performing controlled potential electrolysis using electrolytic
reduction apparatuses produced in Example 1 and Comparative Example
1, respectively, in Test Example 1.
FIG. 4 is a spectrogram showing Raman spectra of deposits obtained
by performing controlled potential electrolysis using electrolytic
reduction apparatuses produced in Example 2 and Comparative Example
2, respectively, in Test Example 1.
DESCRIPTION OF EMBODIMENTS
Technical Problem
When electrolytic reduction of carbon dioxide is performed,
sp.sup.2 carbon atoms are more likely to be generated than sp.sup.3
carbon atoms, which can form a diamond structure. Thus, the method
described in Patent Literature 1 has a drawback that it is
difficult to form a diamond structure. The term "sp.sup.2 carbon
atom" refers to a carbon atom forming sp.sup.2 hybrid orbitals in
bonding between carbon atoms. In addition, the term "sp.sup.3
carbon atom" refers to a carbon atom forming sp.sup.3 hybrid
orbitals in bonding between carbon atoms.
The present disclosure has been made in view of such circumstances,
and an object of the present disclosure is to provide a novel
method for manufacturing a carbon material, by which a carbon
material containing diamond can be manufactured at normal pressure
and which is different from electrolytic reduction of carbon
dioxide, and a novel carbon material manufactured by the
manufacturing method.
Advantageous Effects of Invention
According to the present disclosure, a carbon material can be
manufactured at normal pressure without performing electrolytic
reduction of carbon dioxide. In addition, a novel carbon material
can be provided.
SUMMARY OF EMBODIMENTS OF INVENTION
First, contents of embodiments of the present invention will be
listed and described.
(1) A carbon material according to an embodiment of the present
disclosure has at least either a peak related to diamond bonds, or
a peak related to diamond-like bonds, appearing in a range of 1250
to 1400 cm.sup.-1 in a spectrum measured by Raman scattering
spectrometry, and a full width at half maximum of a maximum peak,
or each of full widths at half maximum of the maximum peak and a
second largest peak, among peaks appearing in the range of 1250 to
1400 cm.sup.-1, has a signal less than 100 cm.sup.-1.
The carbon material according to the present embodiment is a novel
carbon material having a specific spectrum in a spectrum measured
by Raman scattering spectrometry.
The peak related to "diamond bonds" is a peak having a maximum
value in the range of not less than 1325 cm.sup.-1 and less than
1335 cm.sup.-1. In addition, the peak related to "diamond-like
bonds" is a peak having a maximum value in the range of not less
than 1335 cm.sup.-1 and less than 1400 cm.sup.-1.
The carbon material according to the embodiment of the present
disclosure contains one or more of diamond, DLC (Diamond-Like
Carbon), and glassy carbon (including amorphous carbon).
Such a carbon material is suitable, for example, as raw materials
for tools and raw materials for abrasion resistance.
(2) Preferably, the carbon material has the peak related to
diamond-like bonds in the spectrum, and
the peak related to diamond-like bonds includes at least one peak
in a range of not less than 1335 cm.sup.-1 and not greater than
1370 cm.sup.-1.
The surface of such a carbon material is flat, and cracking and
chipping are reduced therein, so that the carbon material is more
suitable as raw materials for tools and raw materials for abrasion
resistance.
(3) Preferably, the carbon material has the peak related to diamond
bonds in the spectrum,
the peak related to diamond bonds is in the range of not less than
1325 cm.sup.-1 and less than 1335 cm.sup.-1 and has a full width at
half maximum less than 20 cm.sup.-1, and
an area that does not contain a part of a crystal that is a
hexa-octahedron is present in a portion having a signal of the peak
related to diamond bonds.
Such a carbon material has high surface hardness, cracking and
chipping are reduced therein, and the surface of the carbon
material becomes flat. Thus, the carbon material is further
suitable as raw materials for tools and raw materials for abrasion
resistance.
(4) Preferably, the carbon material is a carbon material formed on
a substrate, and
the peak related to diamond bonds or the peak related to
diamond-like bonds is contained in an area that is equal to or
greater than 10% of an entire main surface of the substrate.
This is because, in this case, when the carbon material is used for
a tool for abrasion resistance or the like, the carbon material is
present on the main surface of the substrate as a carbon material
in a state where the carbon material can resist a compression load
from an opposite material and desired abrasion resistance can be
achieved.
(5) Preferably, the carbon material has a peak related to graphite
bonds or a peak related to graphite-like bonds in a range of 1500
to 1650 cm.sup.-1, and the peak related to diamond bonds or the
peak related to diamond-like bonds has a signal greater than 0.15
in peak ratio as compared to the peak related to graphite bonds or
the peak related to graphite-like bonds appearing in the range of
1500 to 1650 cm.sup.-1.
In this case, a sufficient hardness suitable for raw materials for
tools and raw materials for abrasion resistance can be ensured.
(6) The carbon material preferably contains an alkali metal
element.
This is because, when an alkali metal is contained in a carbon
material having a small lattice interval, carbon bonds are
partially cut, and thus the carbon material becomes a material that
is less likely to induce cracking or fracture.
(7) The carbon material also preferably contains a halogen
element.
This is because, in this case, when the halogen element is present
in a portion where carbon at which bonds are partially cut is
present and it bonds to the carbon, the carbon is stabilized, and a
material that is less likely to cause progress of cracking or
fracture is obtained.
(8) A method for manufacturing a carbon material according to an
embodiment of the present disclosure includes the step of, in a
state where an anode and a cathode having a roughened surface are
disposed in a molten salt electrolytic solution containing
carbonate ions and hydroxide ions in a molten salt, performing
electrolytic reduction of the carbonate ions and the hydroxide ions
contained in the molten salt electrolytic solution, to generate a
carbon material on the cathode.
In the method according to the present embodiment, in a state where
the anode and the cathode are disposed in the molten salt
electrolytic solution containing carbonate ions and hydroxide ions
in a molten salt, electrolytic reduction of the carbonate ions and
the hydroxide ions is performed. Thus, sp.sup.2 carbon atoms and
sp.sup.3 carbon atoms derived from the carbonate ions and adsorbed
hydrogen atoms derived from the hydroxide ions can be generated.
The sp.sup.2 carbon atoms more easily react with the adsorbed
hydrogen atoms than the sp.sup.3 carbon atoms. Therefore, the
sp.sup.2 carbon atom can be removed from the molten salt
electrolytic solution as methane gas, which is a reaction product
with the adsorbed hydrogen atoms. In addition, oxide ions generated
as a result of reduction of the carbonate ions and the hydroxide
ions remain in the molten salt electrolytic solution, but are
oxidized at the anode and can be removed from the molten salt
electrolytic solution as oxygen gas. Accordingly, the existence
ratio of the sp.sup.3 carbon atom on the cathode can be increased.
In addition, in the method according to this embodiment, since the
cathode having the roughened surface is used in the electrolytic
reduction, a carbon material formed from the sp.sup.3 carbon atoms
can be efficiently deposited on the cathode. Therefore, with the
method according to this embodiment, a carbon material having more
sp.sup.3 bonds than in the case without using hydroxide ions under
normal pressure can be manufactured even without performing
electrolytic reduction of carbon dioxide.
(9) The cathode having the roughened surface is preferably a
cathode having a surface roughened by diamond abrasive grains. In
the case of using such a cathode, the proportion of spa bonds in a
deposited carbon material is higher.
(10) The molten salt is preferably a molten salt containing at
least one type of cation selected from the group consisting of
alkali metal ions and alkaline earth metal ions, as a cation, and a
halide anion as an anion. This is because, in the molten salt, the
carbonate ions and the hydroxide ions can be stably present, and
electrolytic reduction of the carbonate ions and the hydroxide ions
can be efficiently performed. In addition, the molten salt is
dissolved at a relatively low temperature, and is stable even after
being melted.
(11) A hydroxide ion concentration of the molten salt electrolytic
solution is preferably not less than 2 mol %. This is because the
amount of adsorbed hydrogen atoms to be generated by electrolytic
reduction is increased and the sp.sup.2 carbon atoms can be more
assuredly removed as methane gas from the molten salt electrolytic
solution.
(12) A method for manufacturing a carbon material according to
another embodiment of the present disclosure includes the step of,
in a state where an anode and a cathode are disposed in a molten
salt electrolytic solution containing carbonate ions and hydroxide
ions in a molten salt, performing electrolytic reduction of the
carbonate ions and the hydroxide ions under a condition that
reaction in which sp.sup.2 carbon atoms and adsorbed hydrogen atoms
are reacted with each other to generate methane gas is promoted, to
generate a carbon material on the cathode.
In the method according to the present embodiment, in the molten
salt electrolytic solution containing carbonate ions and hydroxide
ions in a molten salt, electrolytic reduction of the carbonate ions
and the hydroxide ions is performed under a condition that reaction
in which sp.sup.2 carbon atoms and adsorbed hydrogen atoms are
reacted with each other to generate methane gas is promoted. Thus,
the sp.sup.2 carbon atoms can be more efficiently removed from the
molten salt electrolytic solution, as methane gas that is a
reaction product with the adsorbed hydrogen atoms. Accordingly, the
existence ratio of the sp.sup.3 carbon atoms on the cathode is
increased, and thus a carbon material having more sp.sup.3 bonds
can be obtained on the cathode. Therefore, with the method
according to this embodiment, a carbon material having more
sp.sup.3 bonds than in the case without using hydroxide ions under
normal pressure can be manufactured even without performing
electrolytic reduction of carbon dioxide.
(13) The molten salt is preferably a molten salt containing at
least one type of cation selected from the group consisting of
alkali metal ions and alkaline earth metal ions, as a cation, and a
halide anion as an anion. In this case, the proportion of sp.sup.3
bonds in a deposited carbon material is higher.
(14) A hydroxide ion concentration of the molten salt electrolytic
solution is preferably not less than 2 mol %. This is because,
similar to the above (11), the amount of adsorbed hydrogen atoms to
be generated by electrolytic reduction is increased and the
sp.sup.2 carbon atoms can be more assuredly removed as methane gas
from the molten salt electrolytic solution.
DETAILS OF EMBODIMENTS OF INVENTION
Specific examples of embodiments of the present disclosure will be
described with reference to the drawings as appropriate. The
present disclosure is not limited to these examples but is
indicated by the appended claims, and is intended to include
meaning equivalent to the claims and all modifications within the
scope of the claims.
A method for manufacturing a carbon material according to an
embodiment of the present disclosure includes a step of, in a state
where an anode and a cathode having a roughened surface are
disposed in a molten salt electrolytic solution containing
carbonate ions and hydroxide ions in a molten salt, performing
electrolytic reduction of the carbonate ions and the hydroxide ions
contained in the molten salt electrolytic solution, to generate a
carbon material on the cathode (hereinafter, also referred to as a
"method of Embodiment 1").
A method for manufacturing a carbon material according to another
embodiment of the present disclosure includes a step of, in a state
where an anode and a cathode are disposed in a molten salt
electrolytic solution containing carbonate ions and hydroxide ions
in a molten salt, performing electrolytic reduction of the
carbonate ions and the hydroxide ions under a condition that
reaction in which sp.sup.2 carbon atoms and adsorbed hydrogen atoms
are reacted with each other to generate methane gas is promoted, to
generate a carbon material on the cathode (hereinafter, also
referred to as a "method of Embodiment 2").
A carbon material according to an embodiment of the present
disclosure is a carbon material that can be manufactured by the
method of Embodiment 1 or the method of Embodiment 2, the carbon
material having at least either a peak related to diamond bonds, or
a peak related to diamond-like bonds, appearing in the range of
1250 to 1400 cm.sup.-1 in a spectrum measured by Raman scattering
spectrometry, wherein
a full width at half maximum of the maximum peak, or each of full
widths at half maximum of the maximum peak and the second largest
peak, among peaks appearing in the range of 1250 to 1400 cm.sup.-1,
has a signal less than 100 cm.sup.-1 (hereinafter, also referred to
as a "carbon material of Embodiment 3").
The principle of the methods of Embodiments 1 and 2 will be
described with reference to FIG. 1. In FIG. 1, an electrolytic
reduction apparatus 1 includes an electrolytic bath 11, a molten
salt electrolytic solution 12, an anode 13, a cathode 14, and a
power supply 15. The molten salt electrolytic solution 12 is stored
in the electrolytic bath 11. The molten salt electrolytic solution
12 is an electrolytic solution containing carbonate ions and
hydroxide ions in a molten salt. The anode 13 and the cathode 14
are each disposed in the electrolytic bath 11 so as to be immersed
in the molten salt electrolytic solution 12. The electrolytic
reduction apparatus 1 may further include a heater and a
thermocouple that are not shown, etc.
In the electrolytic reduction apparatus 1, when electricity is
applied between the anode 13 and the cathode 14, the carbonate ions
("CO.sub.3.sup.2-" in the drawing) and the hydroxide ions
("OH.sup.-" in the drawing) in the molten salt electrolytic
solution 12 receive electrons ("e.sup.-" in the drawing) from the
cathode 14. At this time, carbon deposition, hydrogen gas
generation, and methane gas generation progress on the cathode
14.
Reaction during carbon deposition is represented by formula (I):
CO.sub.3.sup.2-+4e.sup.-.fwdarw.C(sp.sup.2+sp.sup.3)+3O.sup.2-
(I)
(wherein "C(sp.sup.2+sp.sup.3)" represents a mixture of sp.sup.2
carbon atoms and sp.sup.3 carbon atoms).
In the reaction represented by formula (I), the carbonate ions are
reduced, whereby sp.sup.2 carbon atoms, sp.sup.3 carbon atoms, and
oxide ions are generated. Among them, the sp.sup.2 carbon atoms are
used in reaction of methane gas generation. Meanwhile, the sp.sup.3
carbon atoms form a diamond structure on the cathode 14.
Accordingly, diamond ("C(sp.sup.3)" in the drawing) is deposited on
the cathode 14.
Reaction during hydrogen gas generation is represented by formulas
(II) to (IV): OH.sup.-+e.sup.-.fwdarw.H.sub.ad+O.sup.2- (II)
H.sub.ad+H.sub.ad.fwdarw.H.sub.2 (III)
H.sub.ad+OH.sup.-+e.sup.-.fwdarw.H.sub.2+O.sup.- (IV)
(wherein "H.sub.ad" represents an adsorbed hydrogen atom).
In the reaction represented by formula (II), the hydroxide ions are
reduced, whereby adsorbed hydrogen atoms ("H.sub.ad" in the
drawing) and oxide ions (not shown) are generated on the cathode
14. The adsorbed hydrogen atoms are used in the reaction
represented by formula (III), the reaction represented by formula
(IV), and reaction for methane gas generation. By the reaction
represented by formula (III) and formula (IV), hydrogen gas is
generated. The generated hydrogen gas is discharged out of the
molten salt electrolytic solution 12.
The reaction for methane gas generation is represented by formula
(V): C(sp.sup.2)+4H.sub.ad.fwdarw.CH.sub.4 (V). In the reaction
represented by formula (V), methane gas is generated by reaction
between the sp.sup.2 carbon atoms generated by the reaction
represented by formula (I) and the adsorbed hydrogen atoms
generated by the reaction represented by formula (II). The
generated methane gas is discharged out of the molten salt
electrolytic solution 12. Accordingly, the sp.sup.2 carbon atoms
generated by the reaction represented by formula (I) are removed
from the molten salt electrolytic solution 12, and the existence
ratio of sp.sup.3 carbon atoms near the cathode increases. Only the
sp.sup.3 carbon atoms form a diamond structure on the cathode
14.
As described above, in the methods of Embodiments 1 and 2, the
following (1) and (2) are simultaneously performed by causing
carbonate ions and hydroxide ions to coexist in a molten salt and
performing electrolytic reduction of the carbonate ions and the
hydroxide ions.
(1) Cause reaction between sp.sup.2 carbon atoms derived from the
carbonate ions and adsorbed hydrogen atoms derived from the
hydroxide ions and remove the sp.sup.2 carbon atoms as methane
gas.
(2) Form a carbon material containing diamond.
Next, conditions, etc., that are common to the methods of
Embodiments 1 and 2 will be described. In the methods of
Embodiments 1 and 2, the interior of the electrolytic bath is made
into an inert gas atmosphere, then a cathode and an anode are
placed therein, a molten salt electrolytic solution is put into the
electrolytic bath, and electrolytic reduction is performed, whereby
the carbon material according to the embodiment of the present
disclosure can be manufactured.
Examples of an inert gas used in the inert gas atmosphere include
argon gas, but the inert gas is not particularly limited.
Examples of the material that forms the cathode include nickel,
titanium, and silicon carbide, but the material is not particularly
limited. Examples of the shape of the cathode include a plate
shape, but the shape is not particularly limited. The surface area
of the cathode can be set as appropriate in accordance with a
desired deposition amount of the carbon material, or the like.
Examples of the anode include a glassy carbon electrode, a graphite
electrode, a boron-doped diamond electrode, a platinum electrode,
an iridium electrode, a ferrite-based oxygen generating electrode,
and a tin oxide-based oxygen generating electrode, but the anode is
not particularly limited. The shape of the anode is not
particularly limited.
The molten salt electrolytic solution can be obtained, for example,
by mixing a carbonate and a hydroxide salt into a molten salt.
The molten salt used in the molten salt electrolytic solution
preferably has a melting point of 250 to 800.degree. C. from the
viewpoint of efficiently removing sp.sup.2 carbon atoms and leaving
only spa carbon atoms. Examples of the molten salt include a molten
salt containing at least one type of cation selected from the group
consisting of alkali metal ions and alkaline earth metal ions, as a
cation, and a halide anion as an anion (hereinafter, also referred
to as a "molten salt A"); and LiCl--KCl, LiCl--KCl--CsCl,
LiF--NaF--KF, KF--KCl, CaCl.sub.2--BaCl.sub.2, LiCl--CaCl.sub.2,
NaCl--CaCl.sub.2, KCl--CaCl.sub.2, and CaCl.sub.2). However, the
molten salt is not particularly limited. Among these molten salts,
the molten salt A is preferable from the viewpoint of more
efficiently depositing the carbon material according to the
embodiment of the present disclosure.
The cation in the molten salt A is at least one type selected from
the group consisting of alkali metal ions and alkaline earth metal
ions. The cation may be any of (i) a combination of a plurality of
types of alkali metal ions, (ii) a combination of a plurality of
types of alkaline earth meal ions, and (iii) a combination of at
least one type of alkali metal ion and at least one type of
alkaline earth metal ion. Examples of the alkali metal ions include
lithium ion, sodium ion, and potassium ion. In addition, examples
of the alkaline earth metal ions include magnesium ion, calcium
ion, strontium ion, and barium ion.
The anion in the molten salt A is halide ion. The anion may be one
type of halide ion or may be a plurality of types of halide ions.
Examples of the halide ions include fluoride ion, chloride ion,
bromide ion, and iodide ion.
Specific examples of the molten salt A include (a) a mixed molten
salt containing a plurality of types of alkali metal halides
(hereinafter, also referred to as a "mixed molten salt a"), (b) a
mixed molten salt containing a plurality of types of alkaline earth
metals (hereinafter, also referred to as a "mixed molten salt b"),
and (c) a mixed molten salt containing at least one type of alkali
metal halide and at least one type of alkaline earth metal halide
(hereinafter, also referred to as a "mixed molten salt c").
Examples of the alkali metal halides include lithium chloride,
sodium chloride, and potassium chloride, but the alkali metal
halides are not particularly limited. Examples of the alkaline
earth metal halides include calcium chloride, strontium chloride,
and barium chloride, but the alkaline earth metal halides are not
particularly limited. Examples of the mixed molten salt a include a
mixed molten salt of lithium chloride and potassium chloride,
LiCl:KCl=20:80 to 80:20 (mole ratio), and preferably a eutectic
composition molten salt LiCl:KCl=58.5:41.5 (mole ratio), but the
mixed molten salt a is not particularly limited. Examples of the
mixed molten salt b include a mixed molten salt of calcium chloride
and barium chloride, CaCl.sub.2:BaCl.sub.2=20:80 to 80:20 (mole
ratio), and preferably a eutectic composition molten salt
CaCl.sub.2:BaCl.sub.2=65:35 (mole ratio), but the mixed molten salt
b is not particularly limited. Examples of the mixed molten salt c
include a mixed molten salt of lithium chloride and calcium
chloride, LiCl:CaCl.sub.2=20:80 to 80:20 (mole ratio), and
preferably a eutectic composition molten salt LiCl:CaCl.sub.2=61:39
(mole ratio), but the mixed molten salt c is not particularly
limited. Among these molten salts A, the eutectic composition
molten salt of lithium chloride and potassium chloride is
preferable from the viewpoint of more efficiently depositing the
carbon material according to the embodiment of the present
disclosure.
Examples of the carbonate include alkali metal carbonates such as
sodium carbonate and potassium carbonate; and alkaline earth metal
carbonates such as calcium carbonate, but the carbonate is not
particularly limited. The carbonate is preferably alkali metal
carbonates and alkaline earth metal carbonates, and more preferably
potassium carbonate, due to ready availability.
Examples of the hydroxide salt include alkali metal hydroxide salts
such as sodium hydroxide and potassium hydroxide; and alkaline
earth metal hydroxide salts such as calcium hydroxide, but the
hydroxide salt is not particularly limited. The hydroxide salt is
preferably alkali metal hydroxide salts and alkaline earth metal
hydroxide salts, and more preferably potassium hydroxide, due to
ready availability.
The hydroxide ion concentration of the molten salt electrolytic
solution is preferably not less than 2 mol % from the viewpoint of
promoting the reaction for methane gas generation to reduce the
amount of a deposit derived from sp.sup.2 carbon atoms in
electrolytic reduction and improving the yield of the carbon
material according to the embodiment of the present disclosure.
The carbonate ion concentration of the molten salt electrolytic
solution is preferably lower than the above hydroxide ion
concentration from the viewpoint of promoting the reaction for
methane gas generation to reduce the amount of a deposit derived
from sp.sup.2 carbon atoms in electrolytic reduction and improving
the yield of the carbon material according to the embodiment of the
present disclosure. Therefore, the carbonate ion concentration of
the molten salt electrolytic solution can be set as appropriate in
accordance with the hydroxide ion concentration.
Presence/absence of generation of diamond can be confirmed, for
example, by presence of a peak at approximately 1333 cm.sup.-1 by
Raman spectrometry, or presence of a crystal of diamond through an
X-ray diffraction method or a scanning electron microscope.
Normally, a sharp peak, having a full width at half maximum of 2 to
10 cm.sup.-1 and arising from spa hybrid orbitals of diamond, being
observed at approximately 1333 cm.sup.-1 in a Raman spectrum can be
an index for generation of diamond.
Next, the method of Embodiment 1 will be described. In the method
of Embodiment 1, a cathode having a roughened surface is used as
the cathode. The cathode having the roughened surface is obtained,
for example, by roughening the surface of a material used for the
cathode with abrasive grains. Examples of the abrasive grains
include diamond abrasive grains and silicon carbide abrasive
grains, but the abrasive grains are not particularly limited. Among
these abrasive grains, diamond abrasive grains are preferable from
the viewpoint of more efficiently generating the carbon material
according to the embodiment of the present disclosure. As the
diamond abrasive grains, for example, trade name: MD500
manufactured by Tomei Diamond Co., Ltd. (central grain diameter
(D.sub.50): 480 to 529 nm), etc., can be used.
The grain diameters of the abrasive grains are preferably not less
than 20 nm and more preferably not less than 50 nm, from the
viewpoint of obtaining a rough surface sufficient to promote
deposition of the carbon material on the cathode. In addition, the
grain diameters of the abrasive grains are preferably not greater
than 5 .mu.m and more preferably not greater than 2 from the
viewpoint of obtaining a rough surface sufficient to promote
deposition of the carbon material on the cathode. The surface
roughness of the cathode can be set as appropriate in accordance
with the grain diameters of abrasive grains to be used.
In the method of Embodiment 1, the temperature of the molten salt
electrolytic solution in performing electrolytic reduction is
preferably not lower than 650.degree. C. from the viewpoint of
promoting the reaction for methane gas generation to reduce the
amount of a deposit derived from sp.sup.2 carbon atoms in
electrolytic reduction and improving the yield of the carbon
material according to the embodiment of the present disclosure. The
upper limit of the temperature of the molten salt electrolytic
solution in performing electrolytic reduction can be set as
appropriate, within a range where volatilization of the liquid
component of the molten salt electrolytic solution can be
inhibited, in accordance with the type of molten salt to be
used.
In the case of increasing the amount of the carbon material to be
generated, the cathode potential in performing electrolytic
reduction is preferably not greater than 1.2 V, more preferably not
greater than 1.1 V, and further preferably not greater than 1.0 V.
In addition, in this case, the cathode potential in performing
electrolytic reduction is preferably not less than 0.5 V from the
viewpoint of improving the yield of the carbon material. The
potential is a potential represented with, as a reference, the
potential of an alkali metal deposited at a cathode limit of the
molten salt electrolytic solution.
In the method of Embodiment 1, electrolytic reduction may be
performed such that the current density in reduction of the
hydroxide ions is higher than the current density in reduction of
the carbonate ions. Accordingly, it is possible to promote the
reaction for methane gas generation to reduce the amount of a
deposit derived from sp.sup.2 carbon atoms.
Next, the method of Embodiment 2 will be described. The method of
Embodiment 2 can be carried out under the same conditions, etc., as
in the method of Embodiment 1, except that electrolytic reduction
of the carbonate ions and the hydroxide ions is performed under a
condition that the reaction in which sp.sup.2 carbon atoms and
adsorbed hydrogen atoms are reacted with each other to generate
methane gas is promoted. In the method according to Embodiment 2,
in the molten salt electrolytic solution, electrolytic reduction of
the carbonate ions and the hydroxide ions is performed under a
condition that the reaction in which sp.sup.2 carbon atoms and
adsorbed hydrogen atoms are reacted with each other to generate
methane gas is promoted. Accordingly, the sp.sup.2 carbon atoms can
be efficiently removed as methane gas, which is a reaction product
with the adsorbed hydrogen atoms, from the molten salt electrolytic
solution. Due to the removal of the sp.sup.2 carbon atoms, the
existence ratio of spa carbon atoms on the cathode increases, and
thus the carbon material can be generated in a larger amount on the
cathode. In the method of Embodiment 2, the cathode that is used in
Embodiment 1 may be used as the cathode, or a cathode, the surface
of which has not been subjected to a roughening treatment, may be
used as the cathode.
Examples of the condition that the reaction in which sp.sup.2
carbon atoms and adsorbed hydrogen atoms are reacted with each
other to generate methane gas is promoted, include: performing
electrolytic reduction using a molten salt electrolytic solution,
the temperature of which exceeds 650.degree. C.; and performing
electrolytic reduction such that the current density in reduction
of the hydroxide ions is higher than the current density in
reduction of the carbonate ions. However, the condition is not
particularly limited.
The carbon material according to the embodiment of the present
disclosure obtained as described above is useful, for example, as
industrial raw materials, and this carbon material can be used as
raw materials for tools, raw materials for abrasion resistance,
etc.
The carbon material of Embodiment 3, which can be manufactured by
the method of Embodiment 1 or the method of Embodiment 2, has at
least either a peak related to diamond bonds, or a peak related to
diamond-like bonds, appearing in the range of 1250 to 1400
cm.sup.-1 in a spectrum measured by Raman scattering spectrometry
(hereinafter, also referred to as a Raman spectrum), and
the full width at half maximum of the maximum peak, or each of the
full widths at half maximum of the maximum peak and the second
largest peak, among peaks appearing in the range of 1250 to 1400
cm.sup.-1 has a signal less than 100 cm.sup.-1.
The Raman spectrum is a spectrum measured using an apparatus
manufactured by Tokyo Instruments, Inc. (excitation light:He--Ne
laser) with wave number resolution: 1.8 cm.sup.-1 and wave number
reproducibility of Raman scattering peaks: 0.5 cm.sup.-1 or
less.
At this time, a Raman shift value (peak value) is calibrated to a
value obtained when a peak of a Raman spectrum of high pressure
synthesis IIa type crystal diamond is set at 1331 cm.sup.-1.
The carbon material of Embodiment 3 is characterized by having at
least one peak in the range of 1250 to 1400 cm.sup.-1 (a range
related to diamond bonds and/or diamond-like bonds: D band) and in
that the full width at half maximum of the maximum peak in this
range is less than 100 cm.sup.-1. It is preferred if the position
of the peak is in this range, since the carbon material is hard. It
is preferred if the full width at half maximum is in this range,
since the hard carbon material becomes harder.
The position of the peak is preferably in the range of 1320 to 1380
cm.sup.-1 and more preferably in the range of 1325 to 1365
cm.sup.-1, from the viewpoint of enhancing the hardness of the
carbon material.
The full width at half maximum is preferably less than 60
cm.sup.-1, more preferably less than 40 cm.sup.-1, further
preferably less than 30 cm.sup.-1, and particularly preferably less
than 20 cm.sup.-1. The carbon material becomes harder and is less
worn when the full width at half maximum is smaller, and thus such
a carbon material is suitable as raw materials for tools and raw
materials for abrasion resistance.
In the carbon material of Embodiment 3, the position of the peak of
the maximum peak is particularly preferably in the range of not
less than 1335 cm.sup.-1 and not greater than 1370 cm.sup.-1. In
this case, the surface of the carbon material becomes flat and has
less cracking or chipping, and thus becomes more preferable as raw
materials for tools and raw materials for abrasion resistance.
In addition to the peak position being in the range of not less
than 1335 cm.sup.-1 and not greater than 1370 cm.sup.-1, it is
similarly preferred to also have a peak in the range of not less
than 1325 cm.sup.-1 and less than 1335 cm.sup.-1 and have peaks at
a plurality of positions. In this case, the carbon material behaves
like a complex material, and thus is less likely to be chipped off
and becomes hard.
In the carbon material of Embodiment 3, particularly preferably,
the position of a peak is in the range of not less than 1325
cm.sup.-1 and less than 1335 cm.sup.-1 and the full width at half
maximum of the peak has a value less than 20 cm.sup.-1, and the
area of a carbon material in which such a peak appears (a spatial
range having the peak in the range of not less than 1325 cm.sup.-1
and less than 1335 cm.sup.-1) does not contain a part of a crystal
that is a hexa-octahedron (a quadrangular, triangular, or hexagonal
flat surface included in the hexa-octahedron). At this time, the
peak in the range of not less than 1325 cm.sup.-1 and less than
1335 cm.sup.-1 is more preferably the maximum peak. In this case,
the carbon material has high surface hardness, and the surface of
the carbon material becomes flat.
Regarding the lower limit of the full width at half maximum of the
peak in the range of not less than 1325 cm.sup.-1 and less than
1335 cm.sup.-1, the full width at half maximum of the peak is
preferably not less than 3 cm.sup.-1, more preferably not less than
5 cm.sup.-1, and further preferably not less than 6 cm.sup.-1. When
the full width at half maximum of the peak is not less than 3
cm.sup.-1, the toughness becomes high; when the full width at half
maximum of the peak is not less than 5 cm.sup.-1, the toughness
becomes higher; and when the full width at half maximum of the peak
is not less than 6 cm.sup.-1, the toughness becomes even
higher.
Meanwhile, regarding the upper limit of the full width at half
maximum of the peak, the full width at half maximum of the peak is
preferably less than 20 cm.sup.-1, more preferably less than 12
cm.sup.-1, and further preferably less than 10 cm.sup.-1. When the
full width at half maximum of the peak is less than 20 cm.sup.-1,
the hardness becomes high; when the full width at half maximum of
the peak is less than 12 cm.sup.-1, the hardness becomes higher;
and when the full width at half maximum of the peak is less than 10
cm.sup.-1, the hardness becomes even higher.
When a carbon material having a peak in the range of not less than
1325 cm.sup.-1 and less than 1335 cm.sup.-1 does not contain a part
of a crystal that is a hexa-octahedron (this mode also includes a
mode in which the entirety of the crystal that is the
hexa-octahedron is not contained), cracking and chipping are
reduced in the carbon material. Thus, the carbon material is
suitable as raw materials for tools and raw materials for abrasion
resistance.
Regarding a conventional crystalline diamond having a peak in the
range of not less than 1325 cm.sup.-1 and less than 1335 cm.sup.-1,
when grains thereof are caused to grow on a substrate, the diamond
normally contains a part of a crystal that is a hexa-octahedron,
and the diamond in this state covers the entire surface of the
substrate. However, the diamond in this state is not necessarily
suitable for tools, and grain boundaries that are clearly present
may cause cracking.
Meanwhile, when the carbon material of Embodiment 3 has a peak in
the range of not less than 1325 cm.sup.-1 and less than 1335
cm.sup.-1 and the area of the carbon material having such a peak
does not contain a part of a crystal that is a hexa-octahedron, the
carbon material maintains hardness required for tools, and is less
likely to be cracked or chipped off. Thus, the carbon material is
suitable as raw materials for tools.
In the carbon material of Embodiment 3, the peak position and the
full width at half maximum are a peak value and a full width at
half maximum that are obtained by curve fitting with least squares
in a Lorentz distribution on the assumption that a substantially
straight background from 1000 cm.sup.-1 to 1800 cm.sup.-1 is
subtracted and at least one peak is present in the range of 1250 to
1400 cm.sup.-1.
More preferably, the values are values obtained by curve fitting on
the assumption that a peak is further present in the range of 1500
to 1650 cm.sup.-1. Further preferably, the values are values
obtained by curve fitting on the assumption that two peaks are
present in the range of 1300 to 1400 cm.sup.-1 and two peaks are
present in the range of 1500 to 1650 cm.sup.-1. More peaks may be
assumed. However, when the number of peaks is not less than four,
the peak position and the full width at half maximum are not
greatly changed even if the number of assumed peaks in curve
fitting is different.
The carbon material of Embodiment 3 may have a film shape formed on
a surface of a substrate. The carbon material is suitable to be
manufactured as a film that is in close contact with a substrate.
Here, as the substrate, for example, the cathode that is used in
the methods of Embodiments 1 and 2 can be used. Such a film-shaped
carbon material is suitable as raw materials for tools, raw
materials for abrasion resistance, and raw materials for tools for
abrasion resistance.
When the carbon material is a film formed on a substrate, the film
thickness thereof is not particularly limited, but is preferably
0.01 .mu.m to 1 mm. From the viewpoint of easy application to
various uses, the film thickness is more preferably 0.1 .mu.m to 50
.mu.m.
In addition, the shape of the substrate (the shape of the surface
thereof) does not necessarily need to be flat, and may be curved.
Even when the substrate surface is curved, the flatness of the film
surface formed by the carbon material after the point that the
substrate surface is curved is subtracted is also good.
When the carbon material is a film formed on a substrate, the size
of the area that satisfies the above Raman spectrum is preferably
not less than 10% of the size of a main surface of the
substrate.
This is because, in this case, when the carbon material is used for
a tool for abrasion resistance or the like, the carbon material is
present on the main surface of the substrate as a carbon material
in a state where the carbon material can resist a compression load
from an opposite material and desired abrasion resistance can be
achieved.
The size of the area is more preferably not less than 20% of the
size of the main surface of the substrate. The 20% is a proportion
at which carbon materials start establishing a network
therebetween. In this case, the carbon material further easily
resists a compression load and has better abrasion resistance.
The size of the area is further preferably not less than 50% of the
size of the main surface of the substrate. In this case, a state is
obtained where the network between the carbon materials is
completely established. Thus, the carbon material particularly
easily resists a compression load and has particularly good
abrasion resistance.
The size of the area is particularly preferably not less than 80%
of the size of the main surface of the substrate.
When the carbon material according to the embodiment of the present
disclosure is made as a film formed on a substrate, the substrate
provided with the carbon material can be used, for example, as a
member for a tool or for abrasion resistance.
In the carbon material, preferably, the Raman spectrum has a peak
related to graphite bonds or a peak related to graphite-like bonds
in the range of 1500 to 1650 cm.sup.-1, and the ratio of the
maximum peak to the maximum peak appearing in the range of 1500 to
1650 cm.sup.-1 (a range related to graphite bonds and/or
graphite-like bonds: G band) (maximum peak in D band/maximum peak
in G band) is greater than 0.15. The ratio of the maximum peak
(maximum peak in D band/maximum peak in G band) is more preferably
not less than 0.3, further preferably not less than 0.6, and
particularly preferably not less than 1.5. This is because, when
the maximum peak appearing in the D band range is larger, the
carbon material is harder and has higher abrasion resistance, and
thus is suitable to be used for a tool.
When the maximum peak appearing in the G band range is large and
the ratio of the maximum peak (maximum peak in D band/maximum peak
in G band) is not greater than 0.15, the carbon material is
flexible as a whole.
The peak related to "graphite bonds" is a peak having a maximum
value in the range of not less than 1500 cm.sup.-1 and less than
1650 cm.sup.-1 and having a full width at half maximum of less than
10 cm.sup.-1. In addition, the peak related to "graphite-like
bonds" is a peak having a maximum value in the range of not less
than 1500 cm.sup.-1 and less than 1650 cm.sup.-1 and having a full
width at half maximum of not less than 10 cm.sup.-1.
The carbon material preferably contains an alkali metal element or
a halogen element. The carbon material particularly preferably
contains sodium, lithium, or chlorine. When the carbon material
contains an alkali metal element or a halogen element, the carbon
material has reduced crack propagation, is less likely to be
cracked or chipped off, and has good durability.
Regarding the lower limit of the content of the alkali metal
element, the content is preferably greater than 0.008 ppm.
Regarding the upper limit of the content of the alkali metal
element, the content is preferably less than 100 ppm. When the
content of the alkali metal element is not less than 100 ppm,
strain on the crystal in the carbon material easily becomes great,
defects such as point defects and holes increase, and the hardness
may decrease.
Regarding the lower limit of the content of the alkali metal
element, the content is more preferably greater than 0.02 ppm and
further preferably greater than 0.08 ppm. On the other hand,
regarding the upper limit of the content of the alkali metal
element, the content is more preferably less than 20 ppm, further
preferably less than 10 ppm, and particularly preferably less than
4 ppm.
Regarding the lower limit of the content of the halogen element,
the content is preferably greater than 0.008 ppm. Regarding the
upper limit of the content of the halogen element, the content is
preferably less than 100 ppm. When the content of the halogen
element is not less than 100 ppm, strain on the crystal in the
carbon material easily becomes great, defects such as point defects
and holes increase, and the hardness may decrease.
Regarding the lower limit of the content of the halogen element,
the content is more preferably greater than 0.02 ppm and further
preferably greater than 0.08 ppm. On the other hand, regarding the
upper limit of the content of the halogen element, the content is
more preferably less than 20 ppm, further preferably less than 10
ppm, and particularly preferably less than 4 ppm.
Regarding the upper limit of the content of the alkali metal and
the halogen element, the total content of the alkali metal and the
halogen element is more preferably less than 100 ppm.
EXAMPLES
Next, the present disclosure will be described in further detail on
the basis of examples, but is not limited to these examples.
Example 1
(1) Preparation of Molten Salt Electrolytic Solution A
178 g of lithium chloride and 222 g of potassium chloride were put
into an alumina crucible (outer diameter 901 mm.times.inner
diameter 84 mm.times.height 120 mm) and mixed therein to obtain a
molten salt raw material. The concentration (mol %) of lithium
chloride in the obtained molten salt raw material was 58.5 mol %.
In addition, the concentration (mol %) of potassium chloride in the
molten salt raw material was 41.5 mol %. Next, the molten salt raw
material was dried under a vacuum condition at 180.degree. C. for 3
days. 2 g of potassium carbonate and 8 g of potassium hydroxide
were added to 400 g of the dried molten salt raw material within a
glove box to obtain a mixture A. A crucible in which the obtained
mixture A was put was placed within a Kanthal cylindrical
container. Thereafter, while argon gas was being supplied into the
cylindrical container at a flow rate of 150 mL/min, the mixture A
within the crucible was heated such that the temperature of the
mixture A reached 650.degree. C., whereby the molten salt raw
material in the mixture A was melted. Accordingly, a molten salt
electrolytic solution A containing a LiCl--KCl eutectic composition
molten salt was obtained. The concentration (mol %) of potassium
carbonate in the molten salt electrolytic solution A is 0.2 mol %.
In addition, the concentration (mol %) of potassium hydroxide in
the molten salt electrolytic solution A is 2.0 mol %.
(2) Production of Plate Electrode
Diamond powder (trade name: MD500 manufactured by Tomei Diamond
Co., Ltd., central grain diameter (D.sub.50): 480 to 529 nm) and
distilled water, the volume of which was substantially equal to
that of the diamond powder, were mixed in a petri dish to obtain an
abrasive grain mixture. The abrasive grain mixture was rubbed
against the surface of a nickel plate (8 mm.times.5 mm.times.0.2
mm) by hand for 1 minute. Next, the surface of the plate was washed
with distilled water, and then washed with ultrasonic waves.
Accordingly, the diamond powder was removed from the surface of the
plate, and a plate electrode was obtained.
(3) Production of Electrolytic Reduction Apparatus
An electrolytic reduction apparatus 20 shown in FIG. 2 was
produced. The electrolytic reduction apparatus 20 includes a
container 21, an electrolytic bath 23, argon gas flow paths 25a and
25b, a heater 27, a working electrode 31a, a working electrode 31b
serving as a cathode, a counter electrode 33 serving as an anode, a
reference electrode 35, a thermocouple 37, and a molten salt
electrolytic solution 41. The heater 27 is provided outside the
container 21. The working electrode 31a is a nickel wire (diameter:
1.0 mm). The counter electrode 33 is a glassy carbon rod (diameter:
5 mm). In addition, the reference electrode 35 is an Ag.sup.+/Ag
electrode. The working electrodes 31a and 31b, the counter
electrode 33, the reference electrode 35, and the thermocouple 37
are disposed within the container 21 such that ends thereof are
immersed in the molten salt electrolytic solution 41 within the
electrolytic bath 23. The argon gas flow paths 25a and 25b are
connected to the container 21. The argon gas flow path 25a is a
flow path for supplying argon gas into the container 21. The argon
gas flow path 25b is a flow path for discharging argon gas out of
the container 21.
In Example 1, the plate electrode obtained in (2) in Example 1 was
used as the working electrode 31b. In addition, in Example 1, the
molten salt electrolytic solution A obtained in (1) in Example 1
was used as the molten salt electrolytic solution 41.
Comparative Example 1
(1) Preparation of Molten Salt Electrolytic Solution B
A molten salt electrolytic solution B was obtained by performing
the same operations as in (1) in Example 1, except that 2 g of
potassium carbonate was added to 400 g of the dried molten salt raw
material instead of adding 2 g of potassium carbonate and 8 g of
potassium hydroxide to 400 g of the dried molten salt raw material.
The concentration (mol %) of potassium carbonate in the molten salt
electrolytic solution B is 0.2 mol %.
(2) Production of Electrolytic Reduction Apparatus
An electrolytic reduction apparatus was produced by performing the
same operations as in (3) in Example 1, except that the molten salt
electrolytic solution B obtained in (1) in Comparative Example 1
was used instead of using the molten salt electrolytic solution A
obtained in (1) in Example 1.
Example 2
(1) Production of Plate Electrode
A plate electrode was obtained by performing the same operations as
in (2) in Example 1, except that a titanium plate (8 mm.times.5
mm.times.0.2 mm) was used instead of using the nickel plate.
(2) Production of Electrolytic Reduction Apparatus
An electrolytic reduction apparatus was produced by performing the
same operations as in (3) in Example 1, except that the plate
electrode obtained in (1) in Example 2 was used instead of using
the plate electrode obtained in (2) in Example 1.
Comparative Example 2
(1) Production of Electrolytic Reduction Apparatus
An electrolytic reduction apparatus was produced by performing the
same operations as in (3) in Example 1, except that the plate
electrode obtained in (1) in Example 2 was used instead of using
the plate electrode obtained in (2) in Example 1, and the molten
salt electrolytic solution B obtained in (1) in Comparative Example
1 was used as the molten salt electrolytic solution 41 instead of
using the molten salt electrolytic solution A obtained in (1) in
Example 1.
Test Example 1
In the following, the electrolytic reduction apparatuses produced
in Examples 1 and 2 and Comparative Examples 1 and 2 were used. The
electrolytic reduction apparatus produced in Example 1 includes the
molten salt electrolytic solution A containing both carbonate ions
and hydroxide ions, and a cathode formed from a nickel plate having
a roughened surface. In addition, the electrolytic reduction
apparatus produced in Example 2 includes the molten salt
electrolytic solution A containing both carbonate ions and
hydroxide ions, and a cathode formed from a titanium plate having a
roughened surface. Meanwhile, the electrolytic reduction apparatus
produced in Comparative Example 1 includes the molten salt
electrolytic solution B containing carbonate ions and not
containing hydroxide ions, and a cathode formed from a nickel plate
having a roughened surface. In addition, the electrolytic reduction
apparatus produced in Comparative Example 2 includes the molten
salt electrolytic solution B containing carbonate ions and not
containing hydroxide ions, and a cathode formed from a titanium
plate having a roughened surface.
Controlled potential electrolysis was performed by applying
electricity between the cathode and the anode of the electrolytic
reduction apparatus at a cathode potential of 1.1 V at 650.degree.
C. until the amount of conducted electricity reached 50 C/cm.sup.2.
The potential is a potential represented with, as a reference, the
potential (Li.sup.+/Li) of metal lithium deposited on the working
electrode 31a.
In this test example and Test Example 2 described later, at the
same potential, the current density was substantially constant, and
the amount of electricity was proportional to time.
A Raman spectrum of a deposit on each cathode was measured under
the above-described conditions using a laser Raman
microspectroscopy apparatus (trade name: Nanofinder 30,
manufactured by Tokyo Instruments, Inc.).
The Raman spectra of the deposits obtained by performing controlled
potential electrolysis using the electrolytic reduction apparatuses
produced in Example 1 and Comparative Example 1 in Test Example 1
are shown in FIG. 3. In FIG. 3, (A) shows the Raman spectrum of the
deposit obtained by performing controlled potential electrolysis
using the electrolytic reduction apparatus produced in Example 1,
and (B) shows the Raman spectrum of the deposit obtained by
performing controlled potential electrolysis using the electrolytic
reduction apparatus produced in Comparative Example 1. In addition,
the Raman spectra of the deposits obtained by performing controlled
potential electrolysis using the electrolytic reduction apparatuses
produced in Example 2 and Comparative Example 2 in Test Example 1
are shown in FIG. 4. In FIG. 4, (A) shows the Raman spectrum of the
deposit obtained by performing controlled potential electrolysis
using the electrolytic reduction apparatus produced in Example 2,
and (B) shows the Raman spectrum of the deposit obtained by
performing controlled potential electrolysis using the electrolytic
reduction apparatus produced in Comparative Example 2. In FIG. 3
and FIG. 4, P.sub.D indicates a peak, in the D band of 1250 to 1400
cm.sup.-1, arising from an sp.sup.3 hybrid orbital, and P.sub.G
indicates a peak, in the G band of 1500 to 1650 cm.sup.-1, arising
from an sp.sup.2 hybrid orbital.
A peak in the range of not less than 1325 cm.sup.-1 and less than
1335 cm.sup.-1 arises from an sp.sup.3 hybrid orbital. In addition,
when the peak in the range of not less than 1325 cm.sup.-1 and less
than 1335 cm.sup.-1 arises from an sp.sup.3 hybrid orbital of
diamond having long range order, the peak is a sharp peak having a
full width at half maximum of 2 to 10 cm.sup.-1. Meanwhile, a peak
at approximately 1580 cm.sup.-1 arises from an sp.sup.2 hybrid
orbital. In addition, a peak at approximately 1360 cm.sup.-1 arises
from an spa hybrid orbital of a diamond-like structure having short
range order. Therefore, when a sharp peak having a full width at
half maximum of 2 to 10 cm.sup.-1 is observed in the range of not
less than 1325 cm.sup.-1 and less than 1335 cm.sup.-1 (see P.sub.D
in the drawing), this peak indicates that the deposit is diamond.
Meanwhile, when a broad peak having a full width at half maximum
exceeding 10 cm.sup.-1 is observed in the range of 1270 cm.sup.-1
to 1380 cm.sup.-1 (see P.sub.D in the drawing), this peak indicates
that the deposit is a diamond-like carbon material in which a
distance for maintaining the order thereof is changed in accordance
with the full width at half maximum. When the distance for the
order is longer, that is, when the full width at half maximum is
smaller, the carbon material becomes harder and is useful as a tool
material. When a peak at approximately 1580 cm.sup.-1 (see P.sub.G
in the drawing) or a broad peak is observed, this peak indicates
that the deposit contains matter that is not diamond.
From the results shown in FIG. 3, it is found that, when the
electrolytic reduction apparatus produced in Example 1 was used, a
sharp peak having a full width at half maximum of 4 cm.sup.-1 is
observed in the range of not less than 1325 cm.sup.-1 and less than
1335 cm.sup.-1, and almost no peak is observed at approximately
1580 cm.sup.-1, in the Raman spectrum of the obtained deposit.
Therefore, it is found that the deposit on the cathode of the
electrolytic reduction apparatus produced in Example 1 is diamond.
On the other hand, it is found that, when the electrolytic
reduction apparatus produced in Comparative Example 1 was used, a
broad peak having a full width at half maximum of 60 cm.sup.-1 is
observed in the range of not less than 1325 cm.sup.-1 and less than
1335 cm.sup.-1, and a peak having a full width at half maximum of
20 cm.sup.-1 is observed at approximately 1580 cm.sup.-1, in the
Raman spectrum of the obtained deposit. Here, the intensity ratio
(the former/the latter) is about 0.1. Therefore, the deposit on the
cathode of the electrolytic reduction apparatus produced in
Comparative Example 1 does not have diamond bonds having a small
full width at half maximum (<5 cm.sup.-1), and the Raman
sensitivity of a carbon material having diamond bonds or
diamond-like bonds having a large full width at half maximum
(.gtoreq.5 cm.sup.-1) is equal to or less than half that of a
material having sp.sup.2 bonds, and thus it is found that these
carbon materials are less than 5%. From these results, it is found
that, by performing electrolysis using, as a medium, the molten
salt electrolytic solution A containing both carbonate ions and
hydroxide ions, diamond is deposited on the cathode formed from the
nickel plate.
From the results shown in FIG. 4, it is found that, when the
electrolytic reduction apparatus produced in Example 2 was used, a
sharp peak having a full width at half maximum of 4 cm.sup.-1 is
observed in the range of not less than 1325 cm.sup.-1 and less than
1335 cm.sup.-1 (see P.sub.D in the drawing), and a weak peak is
merely observed at approximately 1580 cm.sup.-1 (see PG in the
drawing), in the Raman spectrum of the obtained deposit. Therefore,
it is found that the deposit on the cathode of the electrolytic
reduction apparatus produced in Example 2 is a mixture that
contains, as a main component, a carbon material having diamond
bonds having a small full width at half maximum (<5 cm.sup.-1)
and contains a slight amount of a carbon material including
graphite bonds or graphite-like bonds. On the other hand, it is
found that, when the electrolytic reduction apparatus produced in
Comparative Example 2 was used, a broad weak peak having a full
width at half maximum of 120 cm.sup.-1 is observed in the range of
not less than 1325 cm.sup.-1 and less than 1335 cm.sup.-1, and a
broad weak peak having a full width at half maximum of 80 cm.sup.-1
is observed at approximately 1580 cm.sup.-1, in the Raman spectrum
of the obtained deposit. Therefore, the deposit on the cathode of
the electrolytic reduction apparatus produced in Comparative
Example 2 is not a carbon material having diamond bonds having a
small full width at half maximum (<5 cm.sup.-1) but a carbon
material close to DLC having diamond bonds or diamond-like bonds
having a large full width at half maximum (.gtoreq.5
cm.sup.-1).
From these results, it is found that, by performing electrolysis
using, as a medium, the molten salt electrolytic solution A
containing both carbonate ions and hydroxide ions, diamond is
deposited on the cathode formed from the titanium plate.
In the Raman spectrum of the embodiment of the present invention, a
small full width at half maximum indicates high order of
crystallinity, and a large full width at half maximum indicates low
order of crystallinity.
Test Example 2
Other samples were produced by using the method in Test Example 1
and further conducting an experiment for obtaining a deposit using
either one of the electrolytic reduction apparatuses of Examples 1
and 2, and evaluation was performed using the obtained samples.
Samples 1 to 8
Samples 1 to 8 were obtained by the above-described method. For the
obtained samples 1 to 8, a Raman spectrum was measured.
Furthermore, the samples 1 to 8 were observed for "whether a part
of a crystal that is a hexa-octahedron is contained", measured for
"Vickers hardness", and evaluated for "presence/absence of cracking
or chipping". These results are shown in Table 1.
The samples 1 to 4 are deposits obtained using the electrolytic
reduction apparatus of Example 1, and the samples 5 to 8 are
deposits obtained using the electrolytic reduction apparatus of
Example 2.
Furthermore, Table 1 also shows the results of a Raman spectrum of
a reference sample Z produced by the following method.
Reference sample Z: diamond having a thickness of 10 .mu.m produced
on a silicon substrate using a vertical quartz tube type microwave
CVD apparatus (using a quartz tube having a diameter of 46 mm)
under conditions of a pressure of 40 Torr; a substrate temperature
of 850.degree. C.; a power of 300 W; and a mole ratio of methane
gas to hydrogen gas being 6%.
TABLE-US-00001 TABLE 1 D: 1250 to 1400 (cm.sup.-1) G: 1500 to 1650
(cm.sup.-1) Full Full Full Full width width width width Presence/
at half Position at half at half at half absence Position maximum
of maximum Position maximum Position maximum of part Presence/ of
of second of second of of of second of second of crys- absence
maximum maximum largest largest maximum maximum largest largest tal
that Vickers of crack- peak peak peak peak peak peak peak peak is
hexa- hardness ing or (cm.sup.-1) (cm.sup.-1) (cm.sup.-1)
(cm.sup.-1) (cm.sup.-1) (cm.sub.-1) (- cm.sup.-1) (cm.sup.-1) D/G
octahedron (GPa) chipping Sam- 1333 19 -- -- 1580 22 1620 11 2 Not
90 None ple 1 contained Sam- 1350 29 -- -- 1580 25 1620 15 1 Not 85
None ple 2 contained Sam- 1333 11 -- -- 1580 30 1620 25 4 Not 90
None ple 3 contained Sam- 1331 4.6 -- -- 1579 81 -- -- 3.7 Not 90
None ple 4 contained Sam- 1331 4.3 1350 47 1580 28 -- -- 2.3 Not 95
None ple 5 contained Sam- 1331 3.9 1349 88 1557 430 -- -- 1.5 Not
90 None ple 6 contained Sam- 1352 35 1330 9 1580 28 -- -- 0.7 Not
80 None ple 7 contained Sam- 1331 5.1 1349 41 1581 86 -- -- 6.9 Not
90 None ple 8 contained Refer- 1355 110 1331 7 1570 90 -- -- 2.8
Contained 60 None ence sam- ple Z
In Table 1, the "position of maximum peak" at the 1250 to 1400
(cm.sup.-1) field is the Raman shift value of the peak indicating
the maximum Raman intensity among peaks appearing in the range of
1250 to 1400 (cm.sup.-1). The "full width at half maximum of
maximum peak" at the same field is the full width at half maximum
of the peak indicating the maximum intensity. The "position of
second largest peak" at the same field is the Raman shift value of
the peak indicating the highest Raman intensity next to that of the
maximum peak among the peaks appearing in the range of 1250 to 1400
(cm.sup.-1), and the "full width at half maximum of second largest
peak" at the same field is the full width at half maximum of the
second largest peak indicating the highest Raman intensity next to
that of the maximum peak.
The "position of maximum peak" at the 1500 to 1650 (cm.sup.-1)
field is the Raman shift value of the peak indicating the maximum
Raman intensity among peaks appearing in the range of 1500 to 1650
(cm.sup.-1). The "full width at half maximum of maximum peak" at
the same field is the full width at half maximum of the peak
indicating the maximum intensity. In addition, the "position of
second largest peak" at the 1500 to 1650 (cm.sup.-1) field is the
Raman shift value of the peak indicating the highest Raman
intensity next to that of the maximum peak among the peaks
appearing in the range of 1500 to 1650 (cm.sup.-1), and the "full
width at half maximum of second largest peak" at the same field is
the full width at half maximum of the second largest peak
indicating the highest Raman intensity next to that of the maximum
peak.
In Table 1, "D/G" indicates the ratio of the Raman intensity of the
peak indicating the maximum Raman intensity, among the peaks
appearing in the range of 1250 to 1400 (cm.sup.-1), relative to the
intensity of the peak indicating the maximum Raman intensity, among
the peaks appearing in the range of 1500 to 1650 (cm.sup.-1).
For the samples 1 to 8 and the reference sample Z, presence/absence
of a part of a crystal that is a hexa-octahedron was observed using
a SEM. Presence/absence of a part of a crystal that is a
hexa-octahedron was determined on the basis of whether a
triangular, quadrangular, or hexagonal flat surface can be observed
through SEM observation. Specifically, such determination was
performed by the following method.
Observations were made using a SEM at a magnification at which at
least a 10 .mu.m square comes into sight (for example, 1000 to
10000 times). Basically, a carbon material surface having an uneven
surface is confirmed by a fact that the contrast of a surface image
greatly changes within a distance of 1 .mu.m (the average of
brightness is less than 50% or not less than 150%) and is not
uniform within the surface. On the other hand, if the surface of a
carbon material has a flat surface, the contrast of a surface image
is uniform over a distance of 1 .mu.m or greater (the average of
brightness falls within the range of not less than 50% and less
than 150%), and at least two ridge lines (straight lines) are
confirmed at the edge of the flat surface. At this time, when the
angle at which two ridge lines on a certain flat surface intersect
each other is in the range of 60.+-.5.degree., 90.+-.5.degree., or
120.+-.5.degree., the flat surface is determined to be a part of a
triangular flat surface, a quadrangular flat surface, or a
hexagonal flat surface. When the flat surface is observed, a part
of a crystal that is a hexa-octahedron is determined to be
contained.
The "Vickers hardness" was measured by a general evaluation method
using a normal indenter formed from single crystal diamond. A
measurement value of the Vickers hardness is the average of
measurement values at different positions (five locations) in an
area, where the peak in the range of 1250 cm.sup.-1 to 1400
cm.sup.-1 is present, at substantially the center of each
sample.
"Presence/absence of cracking or chipping" was evaluated by
performing a standard working test using test cutting tools
produced by using the deposits obtained as the samples 1 to 8.
As each cutting tool, a cutting bit having a substantially
triangular top face (cutting face), an edge open angle of
60.+-.10.degree., and an angle of the cutting face and a flank of
not less than 70.degree. and not greater than 80.degree. was
produced using a plate material that was cut out of the deposit
with a desired size and a desired shape. Here, the deposit was
brought into a state of having no chipping of 5 .mu.m or greater.
Regarding the cutting conditions in the working test, aluminum
material A5052 was used as a material to be cut, a cutting speed
was 500 m/min, a cutting amount was 0.1 mm, and a feed speed was
0.01 mm/rev. The working test was conducted under these conditions
for 5 hours. After the working test, presence/absence of chipping
was evaluated on the basis of whether chipping of 5 .mu.m or
greater is present.
Presence/absence of cracking was evaluated on the basis of whether
cracking (a crack equal to or greater than 1/3 of the length of the
deposit) occurs in the cutting bit during any of the cutting bit
production and the working test.
As shown in Table 1, each of the samples 1 to 8 did not contain a
part of a crystal that is a hexa-octahedron.
The Vickers hardnesses of the measured samples 1 to 8 were not less
than 80 GPa. On the other hand, the Vickers hardness of the
reference sample Z was 60 GPa and lower than those of the samples 1
to 8.
The samples 1 to 8 and the reference sample Z were not cracked or
chipped off during the above-described working test. The cutting
conditions in the above-described working test are cutting
conditions under which cracking or chipping may occur in diamond
produced using a conventional chemical vapor deposition method, and
the carbon materials of the samples 1 to 8 are indicated to be
suitable as a raw material for cutting tools and the like. The
reason for this is inferred to be that the carbon materials of the
samples 1 to 8 are each a carbon material having a peak in the
range of 1335 cm.sup.-1 to 1370 cm.sup.-1 or a carbon material
having a peak in the range of not less than 1325 cm.sup.-1 and less
than 1335 cm.sup.-1 and having a peak having a full width at half
maximum greater than the full width at half maximum of conventional
diamond.
(Samples 11 to 13)
Samples 11 to 13 were obtained by the above-described method. For
the obtained samples 11 to 13, measurement of "Vickers hardness"
and evaluation of "presence/absence of cracking or chipping" were
performed by the same methods as the above-described methods. The
results of these are shown in Table 2. The samples 11 to 13 are
deposits obtained using the electrolytic reduction apparatus of
Example 1.
TABLE-US-00002 TABLE 2 D: 1250 to 1400 (cm.sup.-1) G: 1500 to 1650
(cm.sup.-1) Full width Full width Full width at half Full width at
half at half Position maximum at half Position maximum Position
maximum of second of second Position maximum of second of second
Presence/ of maximum of maximum largest largest of maximum of
maximum largest largest Vickers absence of peak peak peak peak peak
peak peak peak hardness cracking or (cm.sup.-1) (cm.sup.-1)
(cm.sup.-1) (cm.sup.-1) (cm.sup.-1) (cm.sup.-1) (- cm.sup.-1)
(cm.sup.-1) D/G (GPa) chipping Sample11 1331 4.5 1350 40 1580 25 --
-- 0.3 80 None Sample12 1352 98 -- -- 1558 400 -- -- 0.16 75 None
Sample13 1331 4 -- -- 1580 30 -- -- 0.12 50 None
In the samples 11 to 13, the values of "D/G" were lower than those
of the samples 1 to 8, but Vickers hardnesses of 50 GPa or greater
were ensured, and cracking or chipping did not occur even during
the above-described working test.
The reason why the values of "DIG" are low in the samples 11 to 13
is considered to be that, for example, pretreatment (roughening) on
the substrate for assisting in growth of a carbon material was
insufficient, or an experiment was conducted with controlled
potential electrolysis but the actually applied voltage during
electrolysis was low.
The results of the samples 11 to 13 demonstrate that the Vickers
hardness can be increased by making "DIG" greater than 0.15, and
can be particularly increased by making "DIG" equal to or greater
than 0.3.
(Samples 21 and 22)
Samples 21 and 22 were obtained by the above-described method. For
the obtained samples 21 and 22, the concentrations of lithium,
potassium, and chlorine were measured. The concentration of each of
the components was measured by using secondary ion mass
spectrometry. In addition, for the samples 21 and 22, measurement
of "Vickers hardness" and evaluation of "presence/absence of
cracking or chipping" were performed by the same methods as the
above-described methods. The results of these are shown in Table 3.
The samples 21 and 22 are deposits obtained using the electrolytic
reduction apparatus of Example 1.
Furthermore, the concentrations of lithium, potassium, and chlorine
in the reference sample Z were measured by the above-described
method, and the results thereof are also shown in Table 3.
TABLE-US-00003 TABLE 3 D: 1250 to 1400 (cm.sup.-1) Full width G:
1500 to 1650 (cm.sup.-1) Full width at half Full width at half
Position maximum at half Position Position maximum of second of
second Position maximum of second of maximum of maximum largest
largest of maximum of maximum largest peak peak peak peak peak peak
peak (cm.sup.-1) (cm.sup.-1) (cm.sup.-1) (cm.sup.-1) (cm.sup.-1)
(cm.sup.-1) (- cm.sup.-1) Sample 21 1348 28 -- -- 1580 24 -- Sample
22 1331 3.7 -- -- -- -- -- Reference 1355 110 1331 7 1570 90 --
sample Z G: 1500 to 1650 (cm.sup.-1) Full width at half maximum
Halogen Presence/ of second Alkali metal element Vickers absence of
largest peak Lithium Potassium Chlorine hardness cracking
(cm.sup.-1) D/G (ppm) (ppm) (ppm) (GPa) or chipping Sample 21 --
1.2 0.8 0.4 2 80 None Sample 22 -- -- 0.5 0.2 0.9 100 None
Reference -- 2.8 <0.1 <0.1 <0.1 60 None sample Z
The results of the samples 21 and 22 demonstrate that the carbon
material according to the embodiment of the present disclosure
containing an alkali metal element or a halogen element is suitable
as raw materials for cutting tools and the like, since cracking or
chipping does not occur in the carbon material even when the carbon
material has high hardness.
(Samples 31 to 34)
Samples 31 to 34 were obtained by the above-described method. For
the obtained samples 31 to 34, a size proportion (%) of an area in
which a carbon material having a peak related to diamond bonds or a
peak related to diamond-like bonds was deposited, relative to the
entire surface of the substrate, was calculated. Mapping data of a
Raman spectrum was obtained, and the size proportion (%) was
calculated on the basis of the obtained mapping data. The samples
31 to 34 are deposits obtained using the electrolytic reduction
apparatus of Example 1.
A reference sample W in which a size ratio of an area in which a
film was formed from a carbon material is 5% was separately
produced.
The method for producing the reference sample W is as follows.
A super hard material (WC--Co) having a binder occupying 5% as an
area ratio was produced on a substrate, then Co was thinly removed
(about 5 .mu.m), and diamond was formed on the surface of the super
hard material. At this time, for forming the diamond, the same
conditions as those for producing the reference sample Z were
adopted except that the substrate temperature was set to
880.degree. C. Thereafter, the diamond on WC was removed by
polishing such that the diamond was left only on Co, to produce the
reference sample W.
For the samples 31 to 34 and the reference sample W, measurement of
"Vickers hardness" was performed by the same method as the
above-described method, and "abrasion resistance" was evaluated by
a method described later. The results are shown in Table 4.
The above evaluation of abrasion resistance was performed by
calculating an amount of abrasion caused when each sample was
rubbed against an Al.sub.2O.sub.3 material under the same load, on
the basis of a reduction in thickness. Specifically, the evaluation
was performed by the following method.
First, each sample was processed into an evaluation sample having a
diameter of 300 .mu.m.
Next, the evaluation sample processed with a diameter of 300 .mu.m
was pressed against a flat alumina substrate under a load of 0.8
MPa and slid in a circular manner at a speed of 5 m/min. After 1
hour, an amount of abrasion was measured.
The same evaluation was performed using a standard sample in which
a diamond film is provided on the entire surface using a raw
material of which 100% is polycrystal diamond, and an amount of
abrasion of the standard sample was measured. The abrasion
resistance of the samples 31 to 34 and the reference sample W was
calculated with the abrasion resistance of the standard sample
being set at 100%.
TABLE-US-00004 TABLE 4 D: 1250 to 1400 (cm.sup.-1) G: 1500 to 1650
(cm.sup.-1) Full width Full width Full width at half at half Full
width at half Abrasion Position maximum Position maximum Position
at half Position maximum resistance of maxi- of maxi- of second of
second of maxi- maximum of second of second Vickers (diamond mum
mum largest largest mum of maximum largest largest hard- 100% peak
peak peak peak peak peak peak peak Area ness ratio) (cm.sup.-1)
(cm.sup.-1) (cm.sup.-1) (cm.sup.-1) (cm.sup.-1) (cm.sup.-1) (-
cm.sup.-1) (cm.sup.-1) D/G (%) (GPa) (%) Sample 31 1333 10 -- --
1582 29 1620 22 1.5 10 95 70 Sample 32 1350 55 -- -- 1580 22 -- --
2 20 80 82 Sample 33 1331 4.3 1350 40 1580 35 -- -- 0.8 50 90 86
Sample 34 1350 28 1331 6 1580 30 -- -- 2.5 80 85 90 Reference 1355
150 1331 7 1575 100 1620 50 0.2 5 60 30 sample W
The results of the samples 31 to 34 and the reference sample W
demonstrate that the abrasion resistance improves when the
proportion of the area occupied by the carbon material having a
peak related to diamond bonds or a peak related to diamond-like
bonds increases.
From the above results, it is found that, in a state where an anode
and a cathode having a roughened surface are disposed in a molten
salt electrolytic solution containing carbonate ions and hydroxide
ions in a molten salt, electrolytic reduction of the carbonate ions
and the hydroxide ions is performed, whereby the carbon material
according to the embodiment of the present disclosure can be
generated on the cathode.
In addition, it is also confirmed that the carbon material
according to the embodiment of the present disclosure has high
hardness and cracking or chipping is less likely to occur
therein.
Example 3
(1) Production of electrolytic reduction apparatus
An electrolytic reduction apparatus was obtained by performing the
same operations as in (3) in Example 1, except that a nickel plate
(a plate, the surface of which had not been roughened) was used
instead of using, in (2) in Example 1, the plate electrode obtained
in (3) in Example 1.
(2) Controlled Potential Electrolysis Operation
Under a condition that reaction between sp.sup.2 carbon atoms and
adsorbed hydrogen atoms is promoted (a condition that the
temperature during electrolysis is not lower than 650.degree. C.,
or a condition that the current density in reduction of the
hydroxide ions is higher than the current density in reduction of
the carbonate ions), controlled potential electrolysis was
performed by applying electricity between the cathode and the anode
at a cathode potential of 1.1 V until the amount of conducted
electricity reached 50 C/cm.sup.2. As the potential, a potential
calibrated with the potential (Li.sup.+/Li) of metal lithium
deposited on the working electrode 31a was used.
A Raman spectrum of a deposit on the cathode was measured under the
above-described conditions using a laser Raman microspectroscopy
apparatus (trade name: Nanofinder 30, manufactured by Tokyo
Instruments, Inc.). The results show that in the Raman spectrum of
the deposit, a sharp peak is observed in the range of not less than
1325 cm.sup.-1 and less than 1335 cm.sup.-1, and a broad peak is
observed or no peak is observed at approximately 1580 cm.sup.-1.
Therefore, the results demonstrate that the deposit is diamond.
From the above results, it is found that, in a state where an anode
and a cathode are disposed in a molten salt electrolytic solution
containing carbonate ions and hydroxide ions in a molten salt,
electrolytic reduction of the carbonate ions and the hydroxide ions
is performed under a condition that reaction between sp.sup.2
carbon atoms and adsorbed hydrogen atoms is promoted (a condition
that the temperature of the molten salt electrolytic solution in
performing electrolytic reduction is a temperature exceeding
650.degree. C., or a condition that the current density in
reduction of the hydroxide ions is higher than the current density
in reduction of the carbonate ions), whereby the carbon material
according to the embodiment of the present disclosure can be
generated on the cathode.
REFERENCE SIGNS LIST
1 electrolytic reduction apparatus 11 electrolytic bath 12 molten
salt electrolytic solution 13 anode 14 cathode 15 power supply 20
electrolytic reduction apparatus 21 container 23 electrolytic bath
25a, 25b argon gas flow path 27 heater 31a working electrode 31b
working electrode (cathode) 33 counter electrode (anode) 35
reference electrode 37 thermocouple 41 molten salt electrolytic
solution
* * * * *